"Many relatives of Wen Jiabao, including his son, daughter, younger brother and brother-in-law, have become extraordinarily wealthy during his leadership," The New York Times reported, quoting an investigation by it on Wen's premiership from 1992-2012.
"A review of corporate and regulatory records indicates that the prime minister's relatives, some of whom have a knack for aggressive deal-making, including his wife, have controlled assets worth at least USD 2.7 billion," it said.
In many cases, the names of the relatives have been hidden behind layers of partnerships and investment vehicles involving friends, work colleagues and business partners, the paper said.
"Untangling their financial holdings provides an unusually detailed look at how politically connected people have profited from being at the intersection of government and business as state influence and private wealth converge in China's fast-growing economy," the report said.
Wen's wife, Zhang Beili, has through her management of state diamond companies helped relatives build a billion- dollar portfolio of investments in insurance, technology and real estate ventures, it said.
Zhang is a geologist with an expertise in gemstones.
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Reacting to the report, the Chinese Foreign Ministry denounced it as a smear campaign against China.
"Some reports smear China and have ulterior motives," Foreign Ministry spokesman Hong Lei said in response to a question about the NYT report.
Wen, 70, has been the Chinese premier for almost 10 years. He is due to step down in a power transition that begins on November 8 when the 18th Party Congress of the ruling Communist Party begins.